89
9151AINDCO07/09
ATA8742
20. 8-bit Timer/Counter0 with PWM
20.1   Features
" Two Independent Output Compare Units
"  Double Buffered Output Compare Registers
"  Clear Timer on Compare Match (Auto Reload)
"  Glitch Free, Phase Correct Pulse Width Modulator (PWM)
"  Variable PWM Period
"  Frequency Generator
"  Three Independent Interrupt Sources (TOV0, OCF0A, and OCF0B)
20.2   Overview
Timer/Counter0 is a general purpose 8-bit Timer/Counter module, with two independent Output
Compare Units, and with PWM support. It allows accurate program execution timing (event man-
agement) and wave generation.
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 20-1 on page 89. For
the actual placement of I/O pins. CPU accessible I/O Registers, including I/O bits and I/O pins,
are shown in bold. The device-specific I/O Register and bit locations are listed in the Register
Description on page 100.
Figure 20-1.  8-bit Timer/Counter Block Diagram 
20.2.1
Registers
The Timer/Counter (TCNT0) and Output Compare Registers (OCR0A and OCR0B) are 8-bit
registers. Interrupt request (abbreviated to Int.Req. in the figure) signals are all visible in the
Timer Interrupt Flag Register (TIFR0). All interrupts are individually masked with the Timer Inter-
rupt Mask Register (TIMSK0). TIFR0 and TIMSK0 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on
the T0 pin. The Clock Select logic block controls which clock source and edge the Timer/Counter
Clock Select
Timer/Counter
OCRnA
OCRnB
=
=
TCNTn
Waveform
Generation
Waveform
Generation
OCnA
OCnB
=
Fixed
TOP
Value
Control Logic
= 0
TOP    BOTTOM
Count
Clear
Direction
TOVn
(Int.Req.)
OCnA
(Int.Req.)
OCnB
(Int.Req.)
TCCRnA
TCCRnB
Tn
Edge
Detector
( From Prescaler )
clk
Tn
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